1. Field of the Invention
The present invention relates to a fabrication method for a liquid crystal display, and more particularly to a fabrication method for a liquid crystal display having at least two pretilt angles.
2. Description of the Related Art
Liquid crystal displays (LCD) are commonly used for flat panel display. Owing to dielectric anisotropy and conductive anisotropy of liquid crystal molecules, molecular orientation of liquid crystals can be shifted under an external electronic field, such that various optical effects are produced.
An LCD panel is generally made up of two substrates, with a certain gap preserved therebetween, and a liquid crystal layer filled within the gap. Respective electrodes are formed on the two substrates, respectively, to control the orientation and orientational shift of liquid crystal molecules.
A TFT (thin film transistor) LCD panel is generally made up of a TFT array substrate and a color filter substrate, and alignment layers are usually disposed on countering sides of the respective substrate to control the alignment of a center-filled liquid crystal layer.
Conventional preparation methods of alignment layers are, for example, evaporation, rubbing and photo-alignment. For large-size panel fabrication, rubbing is still mainly used owing to its mature technology, continuous productivity and low cost.
Rubbing is performed as follows. The countering sides of the upper and lower substrates of an LCD panel are first coated with polymeric solution to form alignment layers. The alignment layers are then rubbed by a covered roller, with a definite orientation created by the directional pile of the covering cloth. By the orientation of the alignment layers, the liquid crystals on the alignment layers are aligned because of molecular actions therebetween. By controlling the rubbing direction of the roller, the liquid crystals are aligned of a certain pretilt angle, benefiting various driving modes of the LCD.
To create multiple domains (of pretilt angle) on the alignment layers, photo-alignment is generally applied, for example, as in Japan Publication Patent No. 10-142608 presented by LG Electron Inc. However, photo-alignment requires polarized light in oblique incidence, resulting in low orientation and anchoring energy. IBM has provided a fabrication method regarding a first-rubbing-latter-exposing process (Japan Publication No. 08-122792), wherein a polarized beam must be applied, and only planar alignment achievable. Even though the pretilt angle may be reduced by breaking polymer side chains in the exposure step, owing to the currently limited polarization provided by a polarizing machine (100% polarized light is hard to obtain), local exposure to the light adversely affects the orientation after rubbing.